The present invention relates to universal joints.
Rotating shafts are commonly used to transmit mechanical energy between different components of a machine. In many instances, either the points at which the shaft is coupled to the components cannot be accurately aligned or those two points move with respect to one another during operation of the machine. In such circumstances, it is commonplace to attach separate shafts to the two components and connect the two shafts together using a universal joint which is capable of transmitting the rotation from one shaft to the other when the shafts are not coaxial.
A typical universal joint has a pair of U-shaped members with their midpoints attached to the end of a different one of the shafts. The open ends of the two U-shaped members are positioned in a facing manner, but rotated at ninety degrees with respect to each other. A cross member is formed by two rods connected at their midpoints and each rod extends between the legs of a different U-shaped member.
One of the drawbacks of this type of joint is the loss in efficiency as the angle between the axes of the two shafts increases. This inefficiency is typified by the output shaft's velocity varying with the angle of rotation. Such velocity variation produces vibration which is of particular concern at higher rotational speeds.
Therefore, it is desirable to be able to couple two non-coaxial shafts in a manner which provides a constant or near constant velocity in the output shaft. This desired function can be expressed as producing a unity ratio of the angular velocity of the two shafts.